The overall objectives of the project are to examine the role that catheptic proteases play in the turnover of specific cellular enzymes during the synchronous cell cycle of the unicellular eukaryote Chlamydomonas reinhardtii. Apart from ascertaining the function of multiple forms of cathepsin D known to occur in this organism, lysosomal vesicles will be isolated from different stages of cell development and the transport and degradation of natural purified protein substrates studied.